The invention relates to a rubber blanket with register cut-outs, and a method of aligning a rubber blanket, more particularly, formed with register cut-outs, relative to a clamping device having register pins, for clamping the rubber blanket onto a cylinder.
Such a method is described in the published German Patent Document DE 35 45 172 A1, corresponding to U.S. Pat. No. 4,707,902, wherein, initially, the ends of a rubber blanket formed with register cut-outs are inserted between clamping bars in a clamping device outside of a printing machine until the register cutouts come into contact with register pins belonging to the clamping devices. The clamping bars of the clamping devices are then connected by clamping screws, The clamping devices with the rubber blanket are then applied to a cylinder in the printing machine.
This method is unsuitable for printing or varnishing machines having clamping devices which are permanently arranged on the cylinder and which serve to fasten a printing plate to the cylinder. Because of the high flexural rigidity of printing plates, they are required to be rolled onto the cylinder, as described, for example, in the published German Patent Document DE 42 14 207 C1, for which purpose clamping devices applied permanently to the cylinder are used.
A rubber blanket corresponding to the rubber blanket generally described in the introduction hereto and in greater detail in the aforementioned published German Patent Document DE 35 45 172 A1 does indeed permit the alignment thereof in-register for cut-out in-line varnishing, but is unfavorable from several points of view because the register cut-outs are introduced directly into the soft blanket material.
On the one hand, the dimensional stability of the register cut-outs is very low. For example, distortion of the register cut-outs cannot be ruled out during frequently repeated fastening of the rubber blanket or because of swelling of the rubber. In addition, the risk exists that cracks will form at the register cut-outs as a result of careless handling of the rubber blanket.
On the other hand, the easily deformable register cut-outs require that the delicate ends of the blanket be aligned and firmly clamped very carefully outside the machine.
In addition, the published German Utility-Model Document DE 94 16 007 U1 describes a rubber blanket having a clamping bar which, in a construction as a flat profile, is vulcanized together with the rubber blanket only on the upper side of the blanket, so that the clamping bar ends flush with an edge of the rubber blanket. The design of the rubber blanket is unfavorable from various points of view.
On the one hand, the rubber blanket is unsuitable for cut-out in-line varnishing because this requires the top rubber layer of the rubber blanket to be cut out in locations corresponding to the varnishing cut-outs, as is extensively described in the aforementioned published German Patent Document DE 35 45 172 A1. Because the rubber blanket does not have any register cut-outs, cutting out the cut-outs in-register is possible only within the printing machine, which is very awkward to do.
On the other hand, the rubber blanket having the clamping bar formed as a flat profile assumes the presence of a clamping device having a maximum opening width, between a clamping pad and a clamping jaw, that is greater than the thickness of the blanket material together with the thickness of the clamping bar connected to the blanket material. Clamping devices which can be closed by rotating a slightly eccentric shaft do not always have such a large opening width, however.
It is accordingly an object of the invention to provide an improved method of aligning a rubber blanket having register cut-outs, and to provide such a rubber blanket which is particularly well suited for performing the method.
With the foregoing and other objects in view, there is consequently provided, in accordance with one aspect of the invention, a method of aligning a rubber blanket formed with register cut-outs, relative to a clamping device having register pins, for clamping the rubber blanket onto a cylinder, which comprises bringing the register cut-outs formed in the rubber cylinder into contact with the register pins of the clamping device when the clamping device has been applied to the cylinder.
In accordance with another aspect of the invention, there is provided a rubber blanket having register cut-outs and being formed of blanket material, comprising a clamping bar of the rubber blanket, the cut-outs being formed in the clamping bar.
In accordance with a further feature of the invention, the clamping bar is disposed only on an underside of the blanket material.
In accordance with an added feature of the invention, the clamping bar projects beyond an edge of the blanket material.
In accordance with an additional feature of the invention, the edge is a leading edge of the blanket material.
In accordance with yet another feature of the invention, the register cut-outs are formed only in the clamping bar.
In accordance with yet a further feature of the invention, the rubber blanket includes a sealing substance provided in at least one corner angle between the blanket material and the clamping bar.
In accordance with yet an added feature of the invention, the rubber blanket includes a clamping device, only the clamping bar being grippable by the clamping device for fastening the rubber blanket to a cylinder.
In accordance with a third aspect of the invention, there is provided a rubber blanket comprising structures defining register cut-outs, the register cut-outs being arranged in the rubber blanket so as to correspond to register cut-outs formed in a printing plate.
In accordance with a fourth and a fifth aspect of the invention, there are provided a printing machine and a varnishing machine, respectively, having a rubber blanket with register cut-outs and being formed of blanket material, the rubber blanket comprising a clamping bar, and the cut-outs being formed in the clamping bar.
Thus, the method according to the invention calls for bringing the register cut-outs in contact with the register pins when the clamping device is applied or fitted to a cylinder.
This method is extremely well suited for printing or by varnishing machines having clamping devices permanently arranged on the cylinder, the clamping devices hating been originally provided only for fastening a printing plate, and being now also selectively used for fastening the rubber blanket. In the method according to the invention, the actions of aligning the register cut-outs in relation to the register pins, and firmly clamping the rubber blanket are performed within the printing or varnishing machine.
The rubber blanket according to the invention is distinguished by the fact that the register cut-outs are introduced into a clamping bar belonging to the rubber blanket.
In this rubber blanket, high dimensional stability of the register cut-outs is assured, which means that multiple in-register clamping of the rubber blanket is possible over a long service life. The clamping bar can be formed as a hard metal strip or plastic strip. For example, in a construction as an aluminum strip, the clamping bar is eminently practical. In order to align the rubber blanket, the register cut-outs introduced into the clamping bar can be brought into engagement with register pins of a clamping device applied or fitted to a cylinder.
In an embodiment which is advantageous with regard to the register cut-outs striking the register pin without tilting, the clamping bar or strip is arranged on the rear side of the blanket material of the rubber blanket, i.e., that side thereof which faces the cylinder and is formed, for example, of a fabric. When the clamping bar or strip is clamped into the clamping device, it therefore rests directly on a clamping pad belonging to the clamping device.
In an embodiment which is advantageous with regard to a clamping device having a small opening width, the clamping bar or strip projects beyond an end of the rubber-covered blanket material which is preferably located at the start of the print. When the rubber blanket is fastened to the cylinder by a clamping device, it is therefore merely necessary for the clamping bar or strip, and not the blanket material, to be inserted into the clamping device and firmly clamped by the latter. The thickness of the clamping bar or strip, which is about 0.3 mm, is several times less than the thickness of the blanket material which is about 2 mm. Because of this fact, the rubber blanket can even be clamped firmly in clamping devices having an opening width which is smaller than the thickness of the rubber blanket.
In an embodiment which is advantageous with regard to the economic production of the clamping bar or strip, only the clamping bar or strip and not the rubber-covered blanket material is provided with the register cut-outs. Although it is also conceivable to stamp the register cut-outs only through the clamping bar or strip or through both the clamping bar or strip and the blanket in the case of a clamping bar or strip that is already permanently connected to the blanket material, it is more beneficial to stamp the register cut-outs into the clamping bar or strip before the clamping bar or strip is connected to the flexible blanket material.
In an embodiment which is advantageous with regard to reducing the risk of the clamping bar or strip loosening or separating from the blanket material, vulcanizing or bonding gaps between the clamping bar or strip and the blanket material are sealed on the outside, for which purpose use can be made again of an adhesive which is already used for the large-area bonding of the clamping bar or strip to the blanket material, or a different adhesive provided specifically for the sealing. The adhesive is applied into the corner angle formed by the blanket material and the clamping bar or strip together, so that the corner angles are partially filled with a wedge of adhesive, and peeling of the soft blanket material off the clamping bar or strip is prevented absolutely reliably, even after a relatively long service time of the rubber blanket.
Sealing is advantageous not only in the case of the clamping bar or strip being connected to the blanket material by adhesive bonding but also in the case of a connection being made by vulcanizing the blanket material onto the clamping bar or strip. In addition to an adhesive or vulcanization bond between the clamping bar or strip and the blanket material, the formlocking connection thereof, for example by rivets, is also conceivable. In this regard, it is noted that a formlocking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a forcelocking connection, which locks the elements together by force external to the elements.
In an embodiment which is advantageous with regard to clamping the rubber blanket into a clamping device in an unyielding and therefore secure manner, only the clamping bar or strip, but not the soft blanket material, is clamped into the clamping device. Because only the flat sides of the clamping bar or strip and either the very soft rubber surface (upper side) nor the fabric surface (underside) of the blanket material are provided as areas for the action of a force or contact areas for the clamping device, there is o danger that there will be any clamping traces pressed persistently into the blanket material, which could have adverse effects upon renewed clamping, even after frequent clamping and unclamping. In addition, it has been shown that a highly permanent bonding of the clamping bar or strip to the blanket material is surprisingly able to withstand the shear loading resulting from the clamping force required to tension or tauten the rubber blanket.
In an embodiment which is advantageous with regard to the variable use of a printing or varnishing-machine cylinder comprising a clamping device with register pins, both the register cut-outs in the rubber blanket and the register cut-outs of a printing plate can be clamped onto the cylinder as a replacement for the rubber blanket and can be pushed in-register onto one and the same register pins belonging to the clamping device. The register cut-outs in the rubber blanket essentially correspond in terms of the shape thereof to the register cut-outs in the printing plate. For example, the center spacing of the register pins is exactly the same as the center spacing of the register cut-outs in the rubber blanket, and exactly the same as the center spacing of the register cut-outs in the printing plate. In the case of a printing plate which, if required, is clamped in register onto the cylinder and, for example, is formed as a flexographic printing plate, the latter can be used for very fine spot varnishing, for example contoured so as to correspond to a line of text. In the case of a rubber blanket, clamped in register onto the cylinder as required, this can be used for varnishing with simply contoured and, for example, rectangular varnishing cut-outs, for which purpose the uppermost rubber layer of the blanket material is cut out so as to coincide with the varnishing cut-outs. Of course, when a blanket is clamped on in the delivered state without making any subsequent cut-outs, the cylinder can also be used for full-surface varnishing and coating.
It is also noted that, in some cases, the register cut-outs in the rubber blanket arranged so as to correspond to the register cut-outs in the printing plate can be introduced into the soft blanket material of a rubber blanket which does not have a clamping bar or strip.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a rubber blanket with register cut-outs, and a method of aligning a rubber blanket, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: